A dual fuel engine can typically operate in two modes. In a strictly liquid fuel mode a liquid fuel, such as diesel fuel, is injected directly into an engine cylinder or a precombustion chamber as the sole source of energy during combustion. In a dual fuel mode a gaseous fuel, such as natural gas, is mixed with air in an intake port of a cylinder and a small amount of diesel fuel is injected into the cylinder or the precombustion chamber in order to ignite the mixture of air and gaseous fuel. In such dual fuel engines, one or more of such gaseous fuel admission valves are positioned between a source of gaseous fuel and an air intake of the engine. When a gaseous fuel admission valve is opened the gaseous fuel passes into the air intake for mixing with the air. Such gaseous fuel admission valves may also be utilized in spark-ignited engines.
A solenoid actuated gaseous fuel admission valve such as that described in U.S. Pat. No. 5,398,724 can be used to deliver the gaseous fuel in such engines. The nature of solenoid actuated gaseous fuel admission valves is such that a current delivered to a solenoid coil thereof actuates the valve. However, problems can arise with such gaseous fuel admission valves, including that it is sometimes possible for such valves to become stuck. For example, typically a solenoid operated valve includes a movable plate and a stationary plate or seat. If even small particulates get trapped between the movable plate and the stationary plate, the two may be positioned far enough apart to allow flow, particularly where the valve is positioned to control the flow of a gaseous fluid. It is desirable in dual fuel engines to be able to determine if a gaseous fuel admission valve is stuck open, or if some other condition is causing gaseous fuel leakage through the valve.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.